Karl du Prel (3 April 1839 – 4 August 1899) was a writer on mysticism and the occult. After serving for the Bavarian army from 1859 to 1872, he began writing about hypnotism and occultism from a psychological point of view. He attempted to prove the existence of spirits through the phenomena of the senses. Karl du Prel was a major figure in Munich art and literature scene of the late nineteenth century. There has been scholarly attention on his works for histories of Spiritism and the occult, literary studies and media theory. Less attention has been given to his contribution on the study of dreams and astronomy.

Karl du Prel considered the unconscious to be an independent and productive entity.[1] The unconscious was seen as being aware of every physiological event in the human body, such as the activity of the vegetative nervous system which the conscious would not be aware of. This concept was later followed with du Prel’s construction of the ‘transcendental subject’. This was the idea that any stimulus must reach a certain threshold in order to achieve consciousness, and whilst conscious the strength of sensation was proportional to the strength of the stimulus. Stimuli that was below the sensory threshold are part of the unconscious mind.

The transcendental subject is the part of the human mind that is active during states of somnambulism and dreaming. Karl du Prel saw the transcendental subject as independent. He believed that one side of our mind experiences the sensory experience of the real world, whilst the other experiences the unconscious world of dreams, trance, telepathy, and clairvoyant vision. Karl du Prel saw these two worlds as separated but not explicitly distinct and isolated.

Karl du Prel explains Spiritism based on the concept of the transcendental object. When one dies, the transcendental and the sensual conscious becomes one. 

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